DAYTONA BEACH — Lionel Stephan graduated 48 years ago from what used to be called the Embry-Riddle School of Aviation, but in all that time he never considered his diploma completely legal.

The school's founders were out of town the day the diploma was signed and the tawny leather document bore the signature of a flight instructor.

On Saturday Stephan, 78, got a bona fide diploma. School founder John Paul Riddle, 85, added his signature during an alumni reunion held at what is now Embry-Riddle Aeronautical University in Daytona Beach.

The diploma will become a part of the school's archives to be a reminder of when a diploma actually lived up to its 'sheepskin' nickname.

''I told John Paul Friday that I had talked to the student affairs dean and he said you're going to give leather diplomas to all the students from now on and John Paul said, 'Forget it,' '' Stephan said, joking.

Embry-Riddle is the only accredited university devoted to aviation in the country. The school has campuses in Daytona Beach, Bunnell, Prescott, Ariz., and satellite operations worldwide. The Daytona Beach campus serves the largest concentration of Embry-Riddle students with an enrollment of 4,850 out of a total of about 11,000 students.

In the years after Stephan paid about $300 for the six-month course provided in 1928, he joined the Embry-Riddle company as a mechanic and later as a pilot. When the company merged into what would become American Airlines, Stephan continued his 40-year career with his only employer.

He retired in 1968 after piloting a commercial supply flight to Vietnam during the war.

Stephan recalls he was one of the few graduates in his class to receive a diploma. He told his flight instructor he wanted proof of graduation. The instructor found a diploma and signed it and told Stephan to take it to the other school officials.

Stephan never got around to making his rounds and eventually he tucked away the diploma in the bottom of an old trunk.

He pulled it out last year when he left his home in Hawaii to attend Embry- Riddle's first alumni reunion in Daytona Beach. That was when he half- jokingly told school officials the diploma still needed a few crucial signatures.

Riddle, who lives in Coral Gables, missed the first reunion. But Stephan later wrote him a letter and Riddle promised to meet him in Daytona Beach this year for the second reunion.

School officials scheduled the signing during the alumni banquet held Saturday.

While attending a barbecue this weekend, Riddle reminisced that Stephan ''was a damn good student because we only hired the best.''